1. Field of the Invention
The present invention relates to a quartz crystal oscillator comprising a quartz crystal tuning fork resonator, capable of vibrating in a flexural mode and having a high frequency stability.
2. Background Information
Quartz crystal oscillators with a quartz crystal tuning fork resonator, which is capable of vibrating in a flexural mode, are widely used as a time standard in consumer products, wearable time-keeping equipment and communication equipment (such as cellular phones, wristwatches and pagers). Recently, because of high stability for frequency, miniaturization and the light weight nature of these products, the need for a smaller quartz crystal oscillator with a smaller quartz crystal tuning fork resonator, capable of vibrating in a flexural mode and having a high frequency stability, a small series resistance and a high quality factor has arisen.
Heretofore, however, it has been impossible to obtain a quartz crystal oscillator with a conventional miniaturized quartz crystal tuning fork resonator, capable of vibrating in a flexural mode, and having a high frequency stability, a small series resistance and a high quality factor. When miniaturized, the conventional quartz crystal tuning fork resonator capable of vibrating in a flexural mode, as shown in FIG. 10 (which has electrodes on the obverse faces 203, 207, reverse faces 204, 208 and the four sides 205, 206, 209, 210 of each tuning fork tine, as also shown in FIG. 11—a cross-sectional view of tuning fork tines of FIG. 10), it has a smaller electromechanical transformation efficiency because the resonator shape and the electrode construction provide a small electric field (i.e. Ex becomes small), as a result of which the resonator has a low frequency stability, a large series resistance and a reduced quality factor. In FIG. 10, a conventional tuning fork resonator 200 is shown with tuning fork tines 201, 202 and a tuning fork base 230.
Moreover, for example, Japanese Patent Nos. P56-65517 and P2000-223992A and International Patent No. WO 00/44092 were published and teach grooves and electrodes constructed at tuning fork tines of a flexural mode, tuning fork, quartz crystal resonator. However, they teach nothing about a quartz crystal oscillator of the present invention having novel shape, novel electrode construction and figure of merit M for a quartz crystal tuning fork resonator, capable of vibrating in a flexural mode and about a relationship of an amplification circuit and a feedback circuit which construct a quartz crystal oscillating circuit, and also, teach nothing about a method for manufacturing a quartz crystal oscillator of the present invention and a quartz crystal unit which is used in the quartz crystal oscillator of the present invention.
In addition, for example, there been has a big problem in the conventional quartz crystal oscillator with the conventional quartz crystal tuning fork resonator, such that a fundamental mode vibration of the resonator jumps to a second overtone mode vibration by shock or vibration.
It is, therefore, a general object of the present invention to provide embodiments of a quartz crystal oscillator comprising a quartz crystal oscillating circuit with a flexural mode, quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode, and having a high frequency stability, a small series resistance and a high quality factor, which overcome or at least mitigate one or more of the above problems.